『C++』Temp_2018_12_26_02

 

 1 #include <iostream>
 2 #include <string>
 3 #include <stdio.h>
 4 #include <stdlib.h>
 5 using namespace std;
 6 
 7 struct Person
 8 {
 9     int age;
10     int id;
11 };
12 
13 template <class T> T myRead(void * memory)
14 {
15     char buffer[sizeof(T)];
16     memcpy(buffer, memory, sizeof(T));
17     T temp = *((T *)buffer);  // 调用 Person 拷贝构造
18     return temp;
19 }
20 
21 template <class T> T myRead2(void * memory)
22 {
23     T temp;
24     memcpy(&temp, memory, sizeof(T));
25     return temp;
26 }
27 
28 template <class T> T* myRead3(void * memory, int offset)
29 {
30     T* temp = new T;
31     memcpy(temp, (char*)memory+offset, sizeof(T));
32     return temp; //返回指针, 有内存泄漏风险
33 }
34 
35 template <class T> void myRead4(void * memory, int offset, T* data)
36 {
37     memcpy(data, (char*)memory+offset, sizeof(T));
38 }
39 
40 template <class T> T* myRead5(void * memory, int offset)
41 {
42     T* t = (T*)((char*)memory+offset);
43     return t;
44 }
45 
46 
47 
48 int main()
49 {
50     char bytes[20] = "\x05\x00\x00\x00\x0A\x00\x00\x00\x06\x00\x00\x00\x0C\x00\x00\x00";
51     Person p = myRead<Person>(bytes);  // 调用 Person 拷贝构造
52     printf("age = %d, id = %d\n", p.age, p.id);
53 
54     Person p2 = myRead2<Person>(bytes);  // 调用 Person 拷贝构造
55     printf("age = %d, id = %d\n", p2.age, p2.id);
56 
57     Person* p3 = myRead3<Person>(bytes, 7);
58     printf("age = %d, id = %d\n", p3->age, p3->id);
59 
60     Person* p4 = new Person;
61     myRead4<Person>(bytes, 7, p4);
62     printf("age = %d, id = %d\n", p4->age, p4->id);
63 
64     //这个会崩溃
65     //Person* p5 = NULL;
66     //myRead4<Person>(bytes, 7, p5);
67     //printf("age = %d, id = %d\n", p5->age, p5->id);
68 
69     Person* p6 = myRead5<Person>(bytes, 7);
70     printf("age = %d, id = %d\n", p6->age, p6->id);
71 
72 
73 
74     cin.get();
75     return 0;
76 }

 

 

执行结果

1 age = 5, id = 10 
2 age = 5, id = 10
3 age = 1536, id = 3072
4 age = 1536, id = 3072
5 //程序崩溃
6 age = 1536, id = 3072

 

posted @ 2018-12-26 17:10  redc  阅读(237)  评论(0)    收藏  举报